Up to now, an ejector has been known as a decompressor applied to a refrigeration cycle device of a vapor compression type. The ejector of this type has a nozzle portion that decompresses refrigerant, sucks a gas-phase refrigerant which flows out from an evaporator by a suction action of an ejected refrigerant ejected from the nozzle portion, mixes the ejected refrigerant with the sucked refrigerant in a pressure increase part (diffuser portion), thereby being capable of boosting the pressure.
Therefore, in the refrigeration cycle device having the ejector as the decompressor (hereinafter referred to as “ejector type refrigeration cycle”), a motive power consumption of the compressor can be reduced with the use of the refrigerant boost action in a pressure increase part of the ejector, and a coefficient of performance (COP) of the cycle can be improved as compared with a normal refrigeration cycle device having an expansion valve as the decompressor.
Further, Patent Document 1 discloses the ejector applied to the refrigeration cycle device with the nozzle portion which decompresses the refrigerant in two stages. In more detail, in the ejector of Patent Document 1, the refrigerant of a high pressure liquid-phase state is decompressed into a gas-liquid two-phase state in a first nozzle, and the refrigerant of the gas-liquid two-phase state flows into a second nozzle.
With the above configuration, in the ejector of Patent Document 1, boiling of the refrigerant in the second nozzle is facilitated to improve a nozzle efficiency as the overall nozzle portion, and the COP is to be further improved as the overall ejector type refrigeration cycle. Meanwhile, the nozzle efficiency represents an energy conversion efficiency in converting a pressure energy of the refrigerant into a kinetic energy in the nozzle portion.